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Large aircraft tail structure by RTM
Processing news
Large aircraft tail structure by RTM THE TOOLING design concepts of North Coast Tool & Mold, Cleveland, Ohio, USA, helped with the resin transfer moulding (RTM) of an all-composite vertical tail developed and manufactured by Lockheed Martin Aeronautics Co. As part of its Advanced Affordability Initiative, Lockheed decided to investigate RTM as a way to reduce costs for large parts like a tail structure, and built three demonstration parts. Its design for the 13 ft long, 5 ft wide part involved two external skins unitised by a series of 14 hollow torque tubes to handle structural loads. The challenge, says North Coast’s president and CEO Rich Petrovich, was to design a tool that could produce such a large, complex part in one shot. “It came down to planning, and it involved not only the tool, but ancillary equipment used for loading the tool, and injecting the part, and a clamp to overcome the injection pressure,” he says. “We think about preform loading, clamping, injection, disassembly, and handling.” The torque tubes, each a unique shape and size, turned out to be a critical cost driver for the project. To create them, North Coast designed a series of interlocking and tapering mandrels using 6061T6 aluminium, slightly undersized to accommodate the reinforcement preform. North Coast counted on thermal expansion of the mandrels against the 4140 mould steel to provide consolidation of the materials. Yet the long, narrow mandrels (90-100 inches in length) proved problematic when it came to developing a
18
REINFORCEDplastics
lay-up approach. Dry broadgoods and prepreg were too costly and complicated. The solution chosen was a triaxial braided sock preform produced by A&P Technology, Cincinnati, Ohio. Because the mandrels’ root ends were several times the size of the tips, standard biaxial braid would have created too much fibre volume at the narrower ends. A&P was able to address this with its MEGABRAIDER™ large braiding machine. Numerical controls adjusted the braid angles during preform fabrication to account for the progressively smaller diameters. To place the braids on the mandrels North Coast developed an ancillary device (a long hookshaped arm). Tail skins were layed up with a combination of fabric and unidirectional tape. Cytec Engineered Materials’ bismaleimide (BMI) resin was used. To address resin flow through all parts of the large mould, North Coast built the mould with directed resin injection and venting (DRIV™) inserts in the skin surfaces. “The inserts help take the ‘black art’ out of the RTM process, they reduce the risk,”
January 2006
states Petrovich. “You don’t want to depend on uncontrolled flooding and you can’t raise injection pressures too high. Higher injection pressure means higher clamping pressures which translates into mould deflection, and the possibility of fibre wash (fabric movement).” The vents are custom engineered to suit the resin viscosity and permit a small amount of resin to flow through to indicate resin flow in that part of the mould. They can be operated manually or automatically. “The inserts enabled better wet-out at lower injection pressure,” states Petrovich. “That meant less material was needed for the mould to overcome injection pressure which reduced overall tooling cost and made the moulds easier to handle and heat.” North Coast designed a costeffective clamp to secure the two mould halves as well as a simple rectangular steel I-beam frame to hold the assembled tool in its upright position. North Coast Tool & Mold; www.nctm.com
CoDA v3.3 released VERSION 3.3 of the CoDA (Composite Component Design Analysis) software package is available from Anaglyph Ltd. CoDA assists in the preliminary stage of engineering design of panels, beams, joints, flanges and laminates, as well as in composite material synthesis.V3.3 offers improved support for sandwich configurations, with calculations for effective honeycomb properties and local skin buckling modes in its panels and beams modules. The laminates module now provides interactive calculations for moisture absorption/desorption, heat throughthickness diffusion and GRP fatigue life. Anaglyph; www.anaglyph.co.uk.
Portable epoxy dispenser A PORTABLE gun for dispensing the two-part epoxies used for insert potting on flameretardant, lightweight honeycomb aircraft interior panels and interiors of trains, boats and other vehicles is available from DTIC Dispensing Technologies. The EZ-mix®HI Dispenser is a battery-powered, motorised hand gun that dispenses 50 ml dual cartridges of epoxy. It dispenses a controlled bead and has a Drip-Free™ design that reduces oozing from the mix tip. The gun is also effective for attaching bonding clips in place and for inserting panel pins. The dispenser costs US$295. DTIC Dispensing Technologies; www.disptech.com
Large aircraft tail structure by RTM THE TOOLING design concepts of North Coast Tool & Mold, Cleveland, Ohio, USA, helped with the resin transfer moulding (RTM) of an all-composite vertical tail developed and manufactured by Lockheed Martin Aeronautics Co. As part of its Advanced Affordability Initiative, Lockheed decided to investigate RTM as a way to reduce costs for large parts like a tail structure, and built three demonstration parts. Its design for the 13 ft long, 5 ft wide part involved two external skins unitised by a series of 14 hollow torque tubes to handle structural loads. The challenge, says North Coast’s president and CEO Rich Petrovich, was to design a tool that could produce such a large, complex part in one shot. “It came down to planning, and it involved not only the tool, but ancillary equipment used for loading the tool, and injecting the part, and a clamp to overcome the injection pressure,” he says. “We think about preform loading, clamping, injection, disassembly, and handling.” The torque tubes, each a unique shape and size, turned out to be a critical cost driver for the project. To create them, North Coast designed a series of interlocking and tapering mandrels using 6061T6 aluminium, slightly undersized to accommodate the reinforcement preform. North Coast counted on thermal expansion of the mandrels against the 4140 mould steel to provide consolidation of the materials. Yet the long, narrow mandrels (90-100 inches in length) proved problematic when it came to developing a
18
REINFORCEDplastics
lay-up approach. Dry broadgoods and prepreg were too costly and complicated. The solution chosen was a triaxial braided sock preform produced by A&P Technology, Cincinnati, Ohio. Because the mandrels’ root ends were several times the size of the tips, standard biaxial braid would have created too much fibre volume at the narrower ends. A&P was able to address this with its MEGABRAIDER™ large braiding machine. Numerical controls adjusted the braid angles during preform fabrication to account for the progressively smaller diameters. To place the braids on the mandrels North Coast developed an ancillary device (a long hookshaped arm). Tail skins were layed up with a combination of fabric and unidirectional tape. Cytec Engineered Materials’ bismaleimide (BMI) resin was used. To address resin flow through all parts of the large mould, North Coast built the mould with directed resin injection and venting (DRIV™) inserts in the skin surfaces. “The inserts help take the ‘black art’ out of the RTM process, they reduce the risk,”
January 2006
states Petrovich. “You don’t want to depend on uncontrolled flooding and you can’t raise injection pressures too high. Higher injection pressure means higher clamping pressures which translates into mould deflection, and the possibility of fibre wash (fabric movement).” The vents are custom engineered to suit the resin viscosity and permit a small amount of resin to flow through to indicate resin flow in that part of the mould. They can be operated manually or automatically. “The inserts enabled better wet-out at lower injection pressure,” states Petrovich. “That meant less material was needed for the mould to overcome injection pressure which reduced overall tooling cost and made the moulds easier to handle and heat.” North Coast designed a costeffective clamp to secure the two mould halves as well as a simple rectangular steel I-beam frame to hold the assembled tool in its upright position. North Coast Tool & Mold; www.nctm.com
CoDA v3.3 released VERSION 3.3 of the CoDA (Composite Component Design Analysis) software package is available from Anaglyph Ltd. CoDA assists in the preliminary stage of engineering design of panels, beams, joints, flanges and laminates, as well as in composite material synthesis.V3.3 offers improved support for sandwich configurations, with calculations for effective honeycomb properties and local skin buckling modes in its panels and beams modules. The laminates module now provides interactive calculations for moisture absorption/desorption, heat throughthickness diffusion and GRP fatigue life. Anaglyph; www.anaglyph.co.uk.
Portable epoxy dispenser A PORTABLE gun for dispensing the two-part epoxies used for insert potting on flameretardant, lightweight honeycomb aircraft interior panels and interiors of trains, boats and other vehicles is available from DTIC Dispensing Technologies. The EZ-mix®HI Dispenser is a battery-powered, motorised hand gun that dispenses 50 ml dual cartridges of epoxy. It dispenses a controlled bead and has a Drip-Free™ design that reduces oozing from the mix tip. The gun is also effective for attaching bonding clips in place and for inserting panel pins. The dispenser costs US$295. DTIC Dispensing Technologies; www.disptech.com